March 2004 • NREL/SR-520-35684 

Process R&D for CIS-Based 

Thin-Film PV 

Annual Technical Report 

24 April 2002–23 April 2003 

D.E. Tarrant and R.R. Gay 

Shell Solar Industries 

Camarillo, California 

National Renewable Energy Laboratory 

1617 Cole Boulevard 

Golden, Colorado 80401-3393 

NREL is a U.S. Department of Energy Laboratory

Operated by Midwest Research Institute • Battelle 

Contract No. DE-AC36-99-GO10337 
March 2004 • NREL/SR-520-35684 

Process R&D for CIS-Based 

Thin-Film PV 

Annual Technical Report 

24 April 2002–23 April 2003 

D.E. Tarrant and R.R. Gay 

Shell Solar Industries 

Camarillo, California 

NREL Technical Monitor: H. S. Ullal 

Prepared under Subcontract No. ZDJ-2-30630-16 

National Renewable Energy Laboratory 

1617 Cole Boulevard 

Golden, Colorado 80401-3393 

NREL is a U.S. Department of Energy Laboratory

Operated by Midwest Research Institute • Battelle 

Contract No. DE-AC36-99-GO10337 
This publication was reproduced from the best available copy

Submitted by the subcontractor and received no editorial review at NREL

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Preface 

Shell Solar Industries (SSI), formerly Siemens Solar Industries has pursued the research and 

development of CuInSe2-based thin film PV technology since 1980. At the start of subcontract 

activities with NREL, SSI had demonstrated a 14.1% efficient 3.4 cm2

 active-area cell, 

unencapsulated integrated modules with aperture efficiencies of 11.2% on 940 cm

2

 and 9.1% on 

3900 cm2, and an encapsulated module with 8.7% efficiency on 3883 cm2 (verified by NREL). 

SSI began a 3-year, 3 phase cost-shared subcontract (No. ZN-1-19019-5) on May 1, 1991 with 

the overall project goal of fabricating a large area, stable, 12.5% aperture efficient encapsulated 

CIS module by scaleable, low-cost techniques on inexpensive substrates. Subcontract 

accomplishments were facilitated by addressing module reproducibility using small area test 

devices and mini-modules. Statistical process control disciplines were adopted to rigorously 

quantify process reproducibility. SSI addressed uniformity and reproducibility of absorber 

formation, interactions of the substrate with the absorber, and performance losses near 

interconnects. Subcontract accomplishments included demonstration of encapsulated module 

efficiencies that were at that time the highest reported mini-module efficiencies for any thin film 

technology (encapsulated 12.8% efficient mini-module on 68.9 cm2

 and an NREL-verified 

12.7% efficient unencapsulated circuit on 69 cm

2

 with a prismatic cover), demonstration of a 

champion large area (3860 cm2

) encapsulated module efficiency of 10.3% (verified by NREL) 

that was the first thin film module of its size to exceed the 10% efficiency level, and delivery to 

NREL of a one kilowatt array of large area (~3890 cm2) approximately 30 watt modules [1]. 

From September 1995 through December 1998, SSI participated in a 3-year, 3 phase cost-shared 

TFPPP subcontract (No. ZAF-5-14142-03). The primary objective of this subcontract was to 

establish reliable high-throughput, high-yield thin film deposition processes in order to make CIS 

a viable option for the next generation of photovoltaics. Outdoor testing, accelerated 

environmental testing, and packaging development progressed throughout all phases of this 

subcontract. During Phase 1, SSI rigorously demonstrating process reproducibility and yield for 

a 10x10-cm monolithically interconnected "mini-module" baseline process and demonstrated a 

13.6% aperture area efficient mini-module (verified by NREL). During Phase 2, SSI 

demonstrated the need to replace an existing large area reactor with a reactor based on a more 

direct scale-up of the baseline reactor, built a new large area reactor, and demonstrated 

comparable performance for the mini-modules baseline and 28x30-cm circuit plates. SSI 

developed products and prototype large area modules using a new package designed to integrate 

small circuit plates into larger modules. A one kilowatt array of Cu (In,Ga)(S,Se)2 modules was 

delivered to NREL replacing a previously installed array based on an older absorber formation 

technology without sulfur incorporated in the absorber (Cu(In,Ga)Se2). This array demonstrated 

significant improvements in efficiency and the temperature coefficient for power. SSI 

introduced two new 5-watt (ST5) and 10-watt (ST10) CIS-based products designed for use in 

12 V systems, and NREL confirmed a new world-record efficiency of 11.1% on a SSI large area 

(3665 cm2

) module. During subcontract Phase 3, substrate size was scaled from ~30x30 cm to 

~30x120 cm and good process control was demonstrated with an average efficiency of 10.8%. 

Commercial product samples were delivered to NREL and a second set of ~30x120 cm modules 

(32 modules totaling ~1.2 kW) was delivered to the NREL Outdoor Test Facility. The NREL 

i 
measured average efficiency at standard test conditions of 11.4% was at that time the highest 

large area efficiency for any thin-film technology and NREL confirmed a world-record 11.8% 

large area (3651 cm2

) efficiency for the champion module [2]. 

From August 1998 through November 2001, SSI participated in a 3-year, 3 phase cost-shared 

TFPPP subcontract (No. ZAF-5-14142-03). The primary objectives of this “Commercialization 

of CIS-Based Thin-Film PV” subcontract were to scale-up substrate size and to increase 

production capacity of the baseline CIS module process while introducing CIS-based products. 

These objectives were pursued to fabricate efficient and stable thin-film modules made by 

scaleable, manufacturable, low-cost techniques. An additional mid- to longer-term objective was 

to advance CIS based thin-film technology thereby assuring future product competitiveness by 

improving module performance, cost per watt produced, and reliability. Throughout this 

subcontract, SSI capabilities were leveraged as a Technology Partner participating in NREL 

team oriented TFPPP activities to address near-term to longer-term R&D topics. SSI’s approach 

to this work was to apply design of experiment and statistical process control methodologies. 

Siemens Solar was the first company in the world to start production of PV modules based on 

CIS thin-film technology and this major milestone in the development of PV was recognized by 

R&D Magazine by awarding the prestigious R&D 100 Award to the Siemens Solar family of 

CIS solar modules. NREL, the California Energy Commission and SSI shared this award. SSI 

expanded the CIS product line in 1999 to include 20-Watt “ST20” modules and 40-Watt “ST40” 

modules. Also during the first subcontract phase, a record-breaking efficiency of more than 12% 

was verified by NREL for an ST-40 module. This result in 1999 far surpassed the DOE year 

2000 goal for a commercial CIS module above 10%. During the second subcontract phase, SSI 

delivered 20 ST-40 large area modules, all with efficiencies over 11%, to meet the subcontract 

deliverables defined as large area modules with efficiencies of over 10%. The average efficiency 

based on a Gaussian fit to the main portion of the circuit plate efficiency distribution was 

increased from 10.8% prior to this subcontract to 11.6% for this subcontract period. These 

advancements were due to continuous improvement of all process along with particular attention 

to process research for two critical processes – CIS formation in new large area reactors and the 

quality of molybdenum deposited in new high capacity sputtering equipment. Process 

development improved adhesion, decreased breakage, addressed control of raw materials, and 

decreased failures associated with patterning. Further R&D of all CIS processes for part size and 

capacity scale-up was pursued during the third subcontract phase. Major accomplishments 

included addressing process issues for implementation of high quality high throughput Mo 

deposition and patterning, high throughput precursor deposition, and higher throughput reaction 

of the precursor. Circuit plate production capacity was increased by more than an order of 

magnitude from the beginning of this subcontract while circuit and module efficiencies were 

steadily improved. The second subcontract milestone – to achieve a pilot production rate 500 

kW per year by the end of subcontract – was first achieved in March of 2001 [3]. 

ii 
Acknowledgments 

Siemens Solar Industries wishes to acknowledge the contributions of the following people and 

organizations. 

The Siemens Solar Industries CIS Team: 

M. Dietrich

O. Frausto 

R. Gay (Program Manager) 

D. Heinemann 

C. Köble 

J. Maher 

P. Norum 

H. Nguyen 

D. Pollock 

Brookhaven National Laboratory 

Colorado State University 

Florida Solar Energy Center 

Fraunhofer Institute / GSF 

A. Ramos 

C. Rischmiller 

U. Rühle 

A. Seapan 

J. Schmitzberger 

D. Tarrant (Principal Investigator) 

S. Voss 

R. Wieting 

D. Willett 

Institute of Energy Conversion / University of Delaware 

National Renewable Energy Laboratory 

Pennsylvania State University 

Showa Shell Seikyu, K.K. 

Shell Solar GmbH 

Washington State University 

iii 
Summary 

Compared to traditional wafer-based crystalline silicon technologies, monolithic integration of 

thin film solar cells can lead to products of comparable performance but with significant 

manufacturing advantages: lower consumption of direct and indirect materials, fewer processing 

steps and easier automation. Monolithic integration is required to achieve these advantages since 

this eliminates multiple process steps and handling operations during formation of the absorber 

and during module assembly. The basic module elements for all thin-film technologies (alloys 

of amorphous silicon, cadmium telluride and CIS) are the same; the module elements are a 

circuit-glass/cover-glass laminate, a frame, and a junction box. The basic circuit elements are 

also very similar; they each have a base electrode, an absorber, a junction, a top electrode and 

three patterning steps for monolithic integration. While the details of these module elements or 

equivalent module elements differ, the basic cost structures are very similar on an area-related 

basis. Since the cost per unit area is the same, the cost per watt is inversely proportional to the 

module efficiency. CIS cells and monolithically integrated modules have demonstrated the 

highest efficiencies of any candidate thin-film technologies; therefore, CIS is expected to have 

the lowest manufacturing cost/watt. 

The primary objectives of this subcontract are to: 

• Address key near-term technical R&D issues for continued CIS product improvement 

• Continue process development for increased production capacity 

• Develop processes capable of significantly contributing to DOE 2020 PV shipment goals 

• Advance mid- and longer-term R&D needed by industry for future product 

competitiveness including improving module performance, decreasing production 

process costs per watt produced, and improving reliability 

• Perform aggressive module lifetime R&D directed at developing packages that address 

the DOE goal for modules that should last up to 30 years while retaining 80% of initial 

power 

Outstanding progress has been made in the initial commercialization of high performance thin 

film CIS technology. During this subcontract period, predictability of SSI’s CIS process was 

demonstrated by continuously executing the process while increasing throughput. Cumulative 

production for 2002 exceeded 1 MW - about twice the production rate for 2001. Average 

laminate efficiency for 2002 is 10.8% with a full width of only 12% of the average. Dramatic 

increases in line yield were achieved from improved production protocols and by addressing 

disparate special causes for process variation. Line yield increased from about 60% in 2000 to 

about 85% in 2002. NREL confirmed a champion 12.8 percent aperture area conversion 

efficiency for a large area (3626 cm2

) CIS production module. Field failure mechanisms for 

prototype modules were clearly demonstrated. Additional circuit plate or packaging process 

variables, although not as clearly established, were also found to effect long-term stability for 

pre-production modules. Significant progress was made toward developing a “glass/glass” 

package that eliminates the TPAT backsheet for decreased cost, simplification of the package 

iv 
and decreased operating temperature. Very promising preliminary results were demonstrated for 

edge seals developed in collaboration with the new NREL sponsored National Thin-Film PV 

Module Reliability Team. Long-term outdoor stability has been demonstrated at NREL where 

~30x30 cm and ~30x120 cm modules with multiple prototype package designs have undergone 

testing for over fourteen years. 

The demonstrated high line yield is the major accomplishment. No one major process 

improvement was responsible for the yield improvements. Judicious application of 

manufacturing engineering disciplines such as SPC, analysis of variation and design of 

experiments led to a clear definition of near term yield issues. Dramatic improvements in yield 

were the result of improving production protocols and addressing disparate special causes for 

process variation. This major accomplishment supports attractive cost projections for CIS. 

Process R&D at successive levels of CIS production has led to the continued demonstration of 

the prerequisites for commitment to large-scale commercialization. SSI's thin-film CIS 

technology is poised to make very significant contributions to DOE/NREL/NCPV long-term 

goals - higher volume, lower cost commercial products. 

v 
Table of Contents 

PREFACE......................................................................................................................................................I 

ACKNOWLEDGMENTS..............................................................................................................................III 

SUMMARY...................................................................................................................................................IV 

TABLE OF CONTENTS ..............................................................................................................................VI 

LIST OF FIGURES .....................................................................................................................................VII 

INTRODUCTION...........................................................................................................................................1 

Overview...................................................................................................................... 1

SSI CIS Process .......................................................................................................... 2 

SSI’s R&D Approach.................................................................................................... 5 

Subcontract Activities and Milestones.......................................................................... 5 

Background .............................................................................................................. 5 

Objectives................................................................................................................. 6 

Milestones ................................................................................................................ 6 

Deliverables.............................................................................................................. 6 

TECHNICAL REVIEW ..................................................................................................................................7 

Process R&D ............................................................................................................... 7 

National CIS R&D Team ............................................................................................ 11 

Package Development............................................................................................... 12 

Glass/Glass Package ............................................................................................. 12 

Outdoor testing ....................................................................................................... 14 

Conclusions ............................................................................................................... 23 

REFERENCES............................................................................................................................................24 

vi 
List of Figures 

Figure 1. Structure of SSI’s monolithically integrated thin-film circuits..............................................1 

Figure 2. SSI’s CIS cell structure (not to scale). .....................................................................................3 

Figure 3. SSI CIS Circuit Processing Sequence. ....................................................................................3 

Figure 4. Typical elemental profile for the SSI graded absorber (SIMS from NREL). .........................4 

Figure 5. Single circuit plate module configuration with a TPAT backsheet.......................................4 

Figure 6. Champion ST40 module from the upper end of the production distribution. .....................7 

Figure 7. Production distribution for 1x4-ft. laminates produced during 2002 ...................................8 

Figure 8. Historical production rate including the first phase of this subcontract (2002). ................8 

Figure 9. Yield improvements...................................................................................................................9 

Figure 10. Laser scribed readable serial number and a 2-dimensional barcode. .............................11 

Figure 11. Present and future package designs. ..................................................................................13 

Figure 12. Darkening and broadening of the interconnects due to moisture ingress......................14 

Figure 13. Demonstrated long-term outdoor stability..........................................................................15 

Figure 14. Normalized changes in FF, ranging from virtually no loss to significant losses, for six 

representative array modules..........................................................................................................16 

Figure 15. Recovery after the thermal exposure of damp heat accelerated tests with or without 

including high humidity in the tests. ..............................................................................................17 

Figure 16. Dirt buildup in a narrow strip at the edge of a wide frame. ...............................................18 

Figure 17. Improperly used tape inside the package. ..........................................................................19 

Figure 18. A laser scan of a thin-film module showing shunting at the edges (Figure 8. from

reference 19 ).....................................................................................................................................20 

Figure 19. 32 Module Arrays: Average Annual Decline ......................................................................21 

vii 
Introduction 

Overview 

Multinary Cu(In,Ga)(Se,S)2 absorbers (CIS-based absorbers) are promising candidates for 

reducing the cost of photovoltaics well below the cost of crystalline silicon. CIS champion solar 

cells have exceeded 18% efficiency for devices fabricated at NREL [4]. Small area, fully 

integrated modules exceeding 13% in efficiency have been demonstrated by several groups [5]. 

Record breaking efficiencies of over 12% for a commercial large area module have been verified 

by NREL [6]. Long-term outdoor stability has been demonstrated at NREL by ~30x30 cm and 

~30x120 cm SSI modules which have been in field-testing for over fourteen years. Projections 

based on current processing indicate production costs well below the cost of crystalline silicon 

[5]. 

Compared to traditional wafer-based crystalline silicon technologies, new thin film technologies 

yield products of comparable performance but with significant advantages in manufacturing 

[5, 7]: 

• Lower consumption of direct and indirect materials 

• Fewer processing steps 

• Easier automation 

Lower consumption of direct and indirect materials results in part from the thin-film structure for 

the semiconductor used to collect solar energy. All three of these manufacturing advantages are 

in part due to an integrated, monolithic circuit design illustrated in Figure 1. Monolithic 

integration eliminates multiple process steps that are otherwise required to handle individual 

wafers and assemble individual solar cells into the final product. 

Glass 

Moly 

CIS 

ZnO CdS 

Figure 1. Structure of SSI’s monolithically integrated thin-film circuits. 

1 
A number of thin film photovoltaic technologies have been developed as alternatives to the 

traditional solar cells based on crystalline silicon wafers [5]. The technologies with the greatest 

potential to significantly reduce manufacturing costs are based on alloys of amorphous silicon 

(a-Si), cadmium telluride (CdTe), CIS, and film silicon (Si-film). These photovoltaic thin film 

technologies have similar manufacturing costs per unit area since all share common elements of 

design and construction: 

• Deposition of typically three layers on a suitable substrate – window/electrode, 

absorber, and back electrode 

• Patterning to create monolithically integrated circuit plates 

• Encapsulation to construct modules 

Cost per watt is a more appropriate figure of merit than cost per unit area [5]. All thin film 

technologies have similar manufacturing costs per unit area since they all use similar or 

equivalent deposition, patterning, and encapsulation processes. About half of the total module 

cost – material, labor, and overhead – originates in the encapsulation scheme which is for the 

most part independent of the thin film technology. Costs for alternative encapsulation schemes 

are typically similar or even higher. The average efficiency of large, ~30x120 cm modules in 

pilot production at Siemens Solar is approximately 11%. This performance is comparable to 

many modules based on crystalline silicon, and is substantially better than the performance 

reported for competing thin-film technologies. The lowest cost per peak watt will result from the 

technology with the highest efficiency, CIS technology, since most thin film technologies have 

similar cost per unit area. 

SSI CIS Process 

Most terrestrial photovoltaic products today are designed to charge a 12-volt battery, however 

the output voltage of an individual solar cell is typically about 0.5 volts. Wafer-based 

technologies build up the voltage by connecting individual solar cells in series. In contrast, CIS 

circuits are fabricated monolithically (Figure 1); the interconnection is accomplished as part of 

the processing sequence to form the solar cell by alternately depositing a layer in the cell 

structure and patterning the layer using laser or mechanical scribing. 

The structure of a SSI CIS solar cell is shown in Figure 2. The full process to form CIS circuit 

plates, including monolithic integration, is outlined in Figure 3. This process starts with ordinary 

sodalime window glass, which is cleaned and an SiO2 barrier layer is deposited to control sodium 

diffusion and improve adhesion between the CIS and the molybdenum (Mo) base electrode. The 

Mo base electrode is sputtered onto the substrate. This is followed by the first patterning step 

(referred to as “P1”) required to create monolithically integrated circuit plates – laser scribing to 

cut an isolation scribe in the Mo electrode. Copper, gallium and indium precursors to CIS 

formation are then deposited by sputtering. Deposition of the precursors occurs sequentially 

from two targets in an in-line sputtering system, first from a copper-gallium alloy target (17 at% 

Ga) and then from a pure indium target. CIS formation is accomplished by heating the 

precursors in H2Se and H2S to form the CIS absorber. Beginning at room temperature, furnace 

temperature is ramped to around 400oC for selenization via H2Se, and ramped again to around 

500oC for subsequent sulfidation via H2S, followed by cool-down to room temperature. This 

deposition of copper and indium precursors followed by reaction to form CIS is often referred to 

2 
as the two-stage process. A very thin coating of cadmium sulfide (CdS) is deposited by chemical 

bath deposition (CBD). This layer is often referred to as a “buffer” layer. A second patterning 

step (P2) is performed by mechanical scribing through the CIS absorber to the Mo substrate 

thereby forming an interconnect via. A transparent contact is made by chemical vapor 

deposition (CVD) of zinc oxide (ZnO). This layer is often referred to as a “window layer” or a 

transparent conducting oxide (TCO). Simultaneously, ZnO is deposited on the exposed part of 

the Mo substrate in the interconnect via and thereby connects the Mo and ZnO electrodes of 

adjacent cells. A third and final patterning step (P3) is performed by mechanical scribing 

through the ZnO and CIS absorber to isolate adjacent cells. 

ZnO 2.2 μm 

CdS 

CIS 

Mo 

Glass 

<0.05 μm 

1.2 μm 

0.35 μm 

2 mm 

Figure 2. SSI’s CIS cell structure (not to scale). 

Prepare 

Substrate 

Deposit 

Precursors 

Deposit 

Base 

Electrode 

Cut 

Isolation 

Scribe 

Absorber 

Formation 

Junction 

Formation 

Cut 

Interconnect 

Via 

Deposit 

Transparent 

Conductor 

Cut 

Isolation 

Via 

Attach 

Leads 

Test 

Light IV 

Figure 3. SSI CIS Circuit Processing Sequence. 

3 
The CIS-based absorber referred to in this report is composed of the ternary compound CuInSe2 

combined with sulfur and gallium to form the multinary compound Cu(In,Ga)(S,Se)2. Gallium 

and sulfur are not uniformly distributed throughout the absorber but the concentrations are 

graded; hence, this structure is referred to as a “graded absorber.” The graded absorber structure 

is a graded Cu(In,Ga)(Se,S)2 multinary with higher sulfur concentration at the front and back and 

higher Ga concentration at the back. Elemental profiles typical of the SSI graded absorber 

structures are presented in Figure 4. Efficiency, voltage, and adhesion improvements have been 

reported for the SSI graded absorber structure [1, 8, 9]. 

Cu 

S 

In 

Se 

Ga 

S 

0 0.5 1 1.5 

Depth (microns) 

Figure 4. Typical elemental profile for the SSI graded absorber (SIMS from NREL). 

Figure 5 illustrates the module configuration used for prototypes and ST products during this 

subcontract period. EVA is used to laminate circuit plates to a tempered cover glass and a 

Tedlar/polyester/Al/Tedlar (TPAT) backsheet provides a hermetic seal. Aluminum extrusions 

are used to build frames for the modules. In addition to providing a hermetic seal, the 

combination of the TPAT backsheet and the offset between the circuit plate and the frame 

provides electrical isolation from the frame. 

Cover Glass Aluminum Frame 

Tedlar/Polyester/Al/Tedlar EVA 

Figure 5. Single circuit plate module configuration with a TPAT backsheet. 

4 
SSI’s R&D Approach 

From the industrial perspective, the full process sequence anticipated for use in large-scale 

production must be mastered and rigorously demonstrated. The SSI research approach is 

composed of two main elements: 

• Experimentation and development using device structures that exercise all aspects of 

large area module production [10] 

• Application of statistical process control (SPC) as the discipline to rigorously 

quantify process reproducibility, and application of statistical methods such as 

analysis of variation (ANOVA) to rigorously quantify experimental results [11, 12]. 

Process predictability is a prerequisite for commercialization of thin-film PV since product 

performance ratings, yields and costs must be known before committing to produce products. 

Also, process predictability is essential for proper interpretation of process development efforts 

since experimental results may be ambiguous or misleading if compared to an unpredictable 

baseline process. SSI has adopted SPC methodologies because SPC was developed to rigorously 

quantify process reproducibility and process capability; the essence of SPC is predictability. 

Equally significantly, SPC provides the measure of systematic progress as processes are 

developed. Communication of this progress is typically best expressed in the language of the 

SPC discipline [13]. For example, process characterization results are demonstrated to be 

“statistically significant” based on knowledge of process repeatability measured using the SPC 

discipline and compared to a predictable baseline process. Confidence in the appropriate 

interpretation of experimental results is gained through application of statistical methods such as 

ANOVA to demonstrate statistically significant results. 

Subcontract Activities and Milestones 

Background 

The purpose of the Thin-Film Photovoltaics Partnerships Program (TFPPP) is to accelerate the 

progress of thin film solar cells and module development as well as to address mid and long-term 

research and development issues. The long-term objective of the TFPPP is to demonstrate 

commercial, low-cost, reproducible, high yield and robust modules of 15% aperture-area 

efficiency. Further more, this research is directed at making progress toward this objective by 

achieving interim goals in thin film module efficiencies; cell and module processing; cell and 

module reliability and the necessary fundamental research needed to build the technology base 

that support these key areas. Participation in the National R&D Teams is paramount to the 

success of this project. The DOE/NREL/NCPV strategy in undertaking this R&D effort is to 

maintain the good coupling between laboratory results from fundamental materials and processes 

research to manufacturing R&D, pilot-line operation, and early entry of advanced thin-film PV 

products to the ever-growing marketplace worldwide. 

The purpose of this subcontract, as part of the Technology Partners Category, is to accelerate the 

progress of thin film solar cell and module development as well as to address mid and long-term 

5 
research and development issues by achieving aggressive interim goals in thin film module 

efficiencies; cell and module processing; cell and module reliability; and in the technology base 

that supports these key areas. 

Objectives 

The primary objectives of this subcontract are to: 

• Address key near-term technical R&D issues for continued CIS product improvement 

• Continue process development for increased production capacity 

• Develop processes capable of significantly contributing to DOE 2020 PV shipment goals 

• Advance mid- and longer-term R&D needed by industry for future product 

competitiveness including improving module performance, decreasing production 

process costs per watt produced, and improving reliability 

• Perform aggressive module lifetime R&D directed at developing packages that address 

the DOE goal for modules that should last up to 30 years while retaining 80% of initial 

power 

Milestones 

SSI shall perform each of the above tasks with the goal of meeting the following targets: 

• Scale the substrate size from 1 ft. X 4 ft. to approximately 2 ft. X 5 ft. by the end of the 

subcontract. 

• Achieve pilot production rates of 9,000 kW per year by the end of the subcontract. 

• Demonstrate commercial, low-cost, reproducible, high yield and robust module process 

that achieve the DOE goal for 15% aperture-area efficiency 

• Deliverables for the subcontract include CIS-based products and representative modules 

delivered to the NREL Module Testing Team for outdoor testing and evaluation. 

Deliverables 

SSI will deliver 10 representative CIS-based module products at the end of each phase of the 

subcontract. 

SSI will deliver 10 representative CIS modules to the NREL Module Testing Team by the end of 

each phase of the subcontract. 

6 
Technical Review

Process R&D 

NREL has confirmed a champion 12.8 percent aperture area conversion efficiency for a large 

area (3626 cm

2

) CIS module (Figure 6). The aperture area for this champion module was 

defined by taping off the approximately 1 cm inactive boarder surrounding the monolithically 

integrated CIS circuit in a ST40, 40 W, production module. Other than definition of the aperture 

area, this module is simply one module from the upper end of the production distribution for 

standard modules. 

Module per Cell 

Eff 12.8 % 

Voc 25.3 0.601 V 

Isc 2.7 A 

Jsc 30.8 mA/cm2 

FF 69.2 % 

* Area 3626 86.3 cm2 

Cells 42 

* Aperture area - including interconnect loss 

Figure 6. Champion ST40 module from the upper end of the production distribution. 

Figure 7 is the production distribution for approximately sixteen thousand ~1x4-ft. laminates 

produced during 2002. The average efficiency of this distribution is 10.8%. A Normal 

distribution fit to the main portion of the distribution yields a standard deviation of 0.66%; over 

88% of this production output is over 10% efficiency. 

7 
15%

10% 

5% 

0% 

0 2 4 6 8 10 12 14 

Aperture Efficiency (%) 

Figure 7. Production distribution for 1x4-ft. laminates produced during 2002 

These champion efficiency and production distribution results are particularly notable since they 

were achieved along with a cumulative production for 2002 of over 1 MW; almost twice the 

production rate for 2001. Historical production rates and the production rate achieved during 

2002, nominally the first phase of this subcontract, are charted in Figure 8. 

1.2 

1.0 

0.8 

0.6 

0.4 

0.2 

0.0 

97 98 99 00 01 02 03 

Year 

Figure 8. Historical production rate including the first phase of this subcontract (2002). 

8 

Production (MW/Year) Percent of Laminates Tested

Normal distribution approximation 

Average = 10.8 % ± 0.66 % 

(Full width is 12% of average) 
Dramatic increases in CIS line yield have been demonstrated [14, 15]. Line yield is defined as 

the ratio of two areas – the area of product produced divided by the area of glass started through 

the production line. This is total yield including both electrical yield and mechanical yield 

through all processing required to produce products. Line yield has increased from about 60% in 

2000 to about 85% in 2002. Process development, guided by SPC approaches, for all process 

steps was required to achieve this high yield. This major accomplishment supports attractive 

cost projections for CIS. 

Figure 9 illustrates yield improvements over approximately the last three years. No one major 

process improvement was responsible for demonstrated yield improvements. Instead, these 

advancements were due to continuous improvement of multiple processes. 

100 

80 

60 

40 

20 

Special Cause 

0 

1999 2000 2001 2002 

Year 

Figure 9. Yield improvements. 

Judicious application of manufacturing engineering disciplines such as SPC, analysis of variation 

and design of experiments led to a clear definition of near term yield issues. Based on this 

guidance, the dramatic improvements in monthly yield through this timeframe were the result of 

improving production protocols and addressing disparate special causes for process variation. 

Significant improvements were made by developing protocols and procedures for sun soaking 

modules prior to final testing. Yield improvements as the result of process development 

included: 

• Decreased breakage at multiple process steps related to handling and process definition CIS Line Yield (%) 

9 
• Elimination of shunting along the laser scribe in the Mo base electrode related to both the 

Mo deposition and laser patterning processes 

• Decreased loss due to equipment failures by improving control systems and production 

procedures 

• Decreased peeling related to glass cleaning, precursor deposition, the reaction process, 

reactor uniformity, and ZnO deposition 

• Decreased peeling related to glass cleaning 

• Decreased peeling related to precursor deposition 

• Decreased peeling related to reaction process conditions 

• Decreased peeling related to reactor uniformity 

• Decreased peeling related to ZnO deposition 

• Decreased loss of process runs by improving infrastructure for higher capacity and yield 

These yield improvements were obtained through repeated cycles of learning. For example, 

improper execution for multiple process steps can lead to peeling. The drop in yield through the 

first half of 2002, Figure 9, was due to peeling. This was found to be due to setup and wear 

issues for a glass washer; issues that are obvious and trivial in hindsight. Finding and addressing 

this special cause lead to the immediate and permanent return to high yield. 

As an example of subcontract work leading to yield improvements, process development led to 

yield improvements for newly implemented equipment [16]. SSI defined the requirements and 

procured laser barcode scribing and barcode reading equipment with the goals of increasing 

capacity by improving productivity and providing high quality data for integrated manufacturing 

infrastructure. Figure 10 illustrates the corner of a circuit plate with both a readable serial 

number for humans and a 2-dimensional barcode for machines. 

10 
Corner of 

circuit plate 

2-dimensional barcode 

Figure 10. Laser scribed readable serial number and a 2-dimensional barcode. 

Process development demonstrated reduced breakage when laser bar codes scribing replaced 

hand scribed serial numbers. A study of yield loss due to breakage during the absorber 

formation process demonstrated that breakage associated with hand scribed serial numbers was 

one of the major causes of breakage. The use of laser scribed bar codes has reduced this kind of 

breakage by 88%. 

National CIS R&D Team 

Prior to and during this subcontract phase SSI contributed to TFPPP National CIS R&D Team. 

Summarizing results for all of the extensive team member activities is not attempted in this 

report since the expertise for most team activities resides with the team members. Instead, the 

following joint NREL/SSI experiments are summarized as examples of teamwork where SSI has 

had major involvement in sample preparation or data analysis. Team activities included: 

• SSI supplied two types of SSI thin-films to TFPPP absorber team members -

complete through Cu(In,Ga)(Se,S)2 absorber formation and complete through ZnO 

deposition. These films were supplied for electrical characterization at NREL and 

IEC, and for compositional analysis at NREL, FSEC, and the University of Illinois. 

• SSI supplied thin-films complete through Cu(In,Ga)(Se,S)2 absorber formation for 

buffer layer experiments at NREL and IEC. 

• SSI deposited CVD ZnO on multiple sets of samples from Larry Olsen, WSU. 

11 
• SSI supplied samples of precursors for reaction pathway measurements at Oak Ridge 

National Laboratories to Suku Kim who is in Tim Anderson’s group at the University 

of Florida. 

• SSI received data from the CIS array at the NREL OTF from Jill Adelstein. A 

summary of this data was included in the final report for the previous subcontract. 

• SSI attended the National CIS R&D Team Meeting held in conjunction with the IEEE 

PV Specialists Conference. 

• Steve Voss represented SSI at the first meeting of the newly formed National Thin 

Film Module Reliability Team Meeting which started with a workshop on moisture 

ingress. Steve presented a talk titled “Accelerated Environmental Testing of Shell 

Solar CIS” 

• SSI participated in team experiments related to identifying the reasons for 

inconsistent performance for SSI absorber only when devices are made with buffer 

and ZnO depositions by NREL or IEC. SSI supplied additional samples of thin-films 

complete through Cu(In,Ga)(Se,S)2 absorber formation for buffer layer experiments 

at NREL and IEC. 

• SSI prepared to supply samples for work on barrier coatings by Larry Olsen at PNNL. 

Package Development 

Glass/Glass Package 

SSI is now developing a “glass/glass” package that eliminates the TPAT backsheet for decreased 

cost, simplification of the package and decreased operating temperature. Figure 11 is a sketch of 

the present production package and the proposed glass/glass package. Simplification of the 

package should increase yield. Decreasing the operating temperature will lead to higher 

efficiency for modules in the field. 

12 
Thin film deleted at 

EVA 

Circuit Plate 

Cover Glass 

Tedlar/Polyester/Al/Tedlar 

Thin Films 

EVA 

Glass / Glass 

Aluminum 

Frame 

Glass / TPAT 

perimeters 

Figure 11. Present and future package designs. 

No detectable humidity ingress occurs during damp heat testing of the current SSI products with 

a TPAT backsheet where damp heat testing refers to an exposure for 1,000 hour at 85oC and 85% 

relative humidity. The new glass/glass package is required to pass accelerated environmental 

tests such as this damp heat test; however, package development indicates that this will require 

additional moisture protection. Figure 12 is a photo of the edge of a glass/glass module where 

the interconnect patterning for monolithic integration is visible as vertical lines above the ruler. 

Darkening and broadening of the interconnects at the edge of the circuit plate is observed for 

glass/glass packages after damp heat testing and has been found to be an indicator of power loss 

due to moisture ingress [17]. This is not observed for the glass/glass package after the same 

thermal exposure but without high humidity. Similarly, the darkening and broadening of the 

interconnects is not observed for production products, that employ a TPAT backsheet and frame, 

after the same thermal exposure with or without high humidity. Edge seal and barrier coatings to 

block humidity ingress are being explored at SSI and in collaboration with the new NREL 

sponsored National Thin-Film PV Module Reliability Team. Preliminary results are very 

promising. 

13 
Figure 12. Darkening and broadening of the interconnects due to moisture ingress. 

Outdoor testing 

FM and UL approval has been obtained for the present package used for the ST series of 

products and the performance of the ST family of CIS thin-film products is backed by a 10-year 

warrantee. Present and potential packages are subjected to both accelerated testing and longterm outdoor testing to develop and improve low cost yet durable packages. One way NREL 

supports SSI in developing products for long-term outdoor reliability is through long term testing 

of arrays and individual modules at the NREL Outdoor Test Facility (OTF). As depicted in 

Figure 13, long-term outdoor stability has been demonstrated at NREL where ~30x30 cm and 

~30x120 cm modules with multiple prototype package designs have undergone testing for over 

fourteen years. 

14 
15 

Siemens Solar Industries CIS Modules

Measured Outdoors At Near STC

0

1

2

3

4

5

6

7

8

9

10

11

12

10/88 10/90 10/92 10/94 10/96 10/98 10/00 10/02

Date

Aperture Efficiency (%)

1988 1988

1990 1990

1992 1992

1994 1994

1998 1998

Note: 1988 modules are 1ft

2

 1990, 92, 94 & 98 are 4ft

2

Taken out of Service

Taken out of Service

Figure 13. ated long-term outdoor stability.

SSI has supplied modules to the NREL OTF for three 1kW arrays. In each case, a newer 

generation of modules has been used to replace older designs using the same test site. 

two arrays demonstrated stability and that thermally induced transients, which are observed after

exposure to high temperatures during accelerated environmental testing, are not observed in the 

field despite daily and seasonal changes in module temperature. nable since 

known transient effects are temperature dependent and the module temperatures reached for 

actual deployment are less than the temperatures defined for accelerated testing. 

Data acquisition began on November 18, 1998 for the third 1kW array of modules. 

is comprised of 28 modules with an average efficiency of 11.4% at STC. erture area of 

each module is 0.3651m2 and of the total array is 10.2 m2. 

true south and is connected to a resistive load through three maximum power trackers. 

Continually logged data is corrected for temperature. 

between 950-1050 W/m

2

 is used for array characterization. NREL measurements indicated array 

performance, normalized to standard test conditions, over 1kW. 

NREL data from late February of 2000 indicated stability within 2% of the measurements made 

shortly after array deployment. ilarly, data for operation through June 30, 1999 indicated 

that the array remained stable with array performance over 1kW. As for previous arrays, both 

module and the array data show good stability with no seasonal variation in performance. 

not be overemphasized that multiple studies have demonstrated that thermally induced transients, 

which are observed after exposure to accelerated environmental testing conditions, are not 

observed in the field. 

More recent continuously logged data from the OTF indicates that the latest array is now 

exhibiting changes with time. up on this observation, NREL made outdoor 

measurements (Daystar) on each module in the array. ix modules were selected for further 

study as representative of the varying of degrees power loss for all array modules. 

provided pulsed simulator (SPIRE), continuous illumination simulator (LACSS), and outdoor 

Demonstr

The first 

This is entirely reaso

The system 

The ap

The array is fixed at a 40° tilt aligned

Only data for incident solar irradiance of 

Sim

It can 

To followS

NREL 
measurement (SOMS) data for the six selected modules (). This data indicates that changes in 

performance are primarily changes in FF. This data also indicates, as is typical of CIS transient 

effects, observed changes are smaller for measurements made with continuous illumination than 

for pulsed simulation. For this sample of six representative modules, the change in FF is highly 

variable ranging from 4% to 18%. The low end of this range is virtually no loss, i.e. within 

measurement variability. The high end of this range is significant and indicated the need for 

additional follow-up. 

0.3 

0.2 

0.1 

0.0 

SPIRE SOMS LACSS 

Measurement Method 

Figure 14. Normalized changes in FF, ranging from virtually no loss to significant losses, for six 

representative array modules. 

Packaging development from early work with mini-modules through ST products has 

demonstrated that thermally induced losses from lamination or accelerated testing will recover 

with extended outdoor exposure [3]. SSI has also demonstrated multiple packaging designs, 

with and without EVA, that protect circuit plates from water vapor ingress during damp heat 

accelerated testing; exposure for 1000 hour at 85oC and 85% relative humidity [2, 3]. CIS circuit 

plates in packages that provide protection from water vapor ingress will pass accelerated 

environmental tests with an outdoor exposure to reverse thermally induced transient effects. 

This conclusion was supported by studies by the NREL TFPPP “Transient Effects Group.” The 

team defined a repeatable measurement methodology for systematic study of thermal transient 

effects that was used to demonstrate reversibility through multiple thermal cycles and thereby 

support outdoor testing results that indicate long term stability for normal operating conditions 

[3, 18]. Based on this foundation, SSI testing indicates that no significant humidity ingress 

occurs during damp heat testing of current SSI products with a TPAT backsheet. Figure 15 is a 

chart of average efficiency for two groups of 8 modules. One group went through the damp heat 

environmental test and the other went through the same temperature cycle but without humidity 

[17]. Both groups were then placed outdoors for 8 weeks of recovery. The two groups show the 

same thermally induced loss and recovery with light exposure; humidity has no impact on the 

results for current SSI products. Normalized FF Chnage 

16 
Efficiency (%) 

12 

Damp 

Dry 

Sun Soak 

Recovery -

Tests after 1 

and 8 weeks 

10

8

6

4

2

0

0 200 400 600 800 1000 0 

Damp heat exposure (hr.) 

Figure 15. Recovery after the thermal exposure of damp heat accelerated tests with or without 

including high humidity in the tests. 

A significant effort has gone into exploring the apparent inconsistency between the most recent 

results from the most recent array of prototype modules deployed at NREL, the most recent 

demonstration of stability for production modules based on accelerated testing, and the combined 

knowledge from multiple sets of accelerated test results, multiple generations of modules 

deployed at NREL and the two previous arrays deployed at NREL that were stable. SSI has 

deployed modules, typically in 1 kW arrays, at test sites throughout the country and, to a lesser 

degree, throughout the world. Modules from multiple sites were retrieved for nondestructive and 

destructive testing to explore the observations from the most recent NREL array. 

Early prototype module designs included a wide frame that extended across the front of the 

modules to cover buss bars. CIS modules have an esthetically pleasing uniform nearly black 

appearance. However, the simplest form of bus bar is a shinny tin-coated copper ribbon. This 

might be an esthetically pleasing combination if the bus bars were uniform but the shinny solder 

used to attach the bus bars yields ragged rather than uniform lines. Wide frames were used in 

pre-production modules to cover the shinny bus bars and solder. The inside edge of these wide 

frames is very close to the outer cells that are narrow strips extending the length of the module; 

parallel with and close to the wide frame. This geometry proved to be very sensitive to dirt 

buildup, Figure 16, in a narrow strip at the edge of frame that shadowed the outer cells. 

Improved performance was demonstrated after scraping away the dirt. However, not all of the 

subset of modules that showed degradation fully recovered after scraping away the dirt. Dirt 

clearly can degrade performance but this mechanism does not explain all degradation. It is 

assumed that the wide frames also tended to trap water, which also could have lead to 

degradation. 

17 
Wide Frame 

Dirt Build-up 

Figure 16. Dirt buildup in a narrow strip at the edge of a wide frame. 

Additional testing demonstrated that errors during fabrication caused degradation for some 

modules and may account for some of the observed OTF array results. In another generation of 

modules, a uniform dark appearance for the front of modules was achieved with narrow frames 

by covering the shinny bus bars with black decorative tape prior to encapsulation. For wide or 

narrow frames, additional tape is used during lay-up for encapsulation to preposition and hold 

the circuit plate, EVA, glass cover sheet and TPAT backsheet. The proper approach is to tape 

together the external components, backsheet to the cover glass, thereby holding all components 

together and allowing the tape to be removed after lamination. However, destructive testing 

found that this tape was at times improperly used to hold internal components i.e. internal 

components were taped to the circuit plate or cover glass before laying up the complete package. 

Therefore, this improperly used tape was partly inside the package during lamination and the 

tape could not be removed after lamination. Instead, after lamination the tape was trimmed off 

with the excess EVA and backsheet. The bond between EVA and the adhesive has never been 

tested for it’s ability to prevent water vapor ingress and EVA does not stick at all to the other 

side of this tape. Therefore, the improperly used tape for lay-up provided a path for water vapor 

penetration past the hermetic seal formed by the combination of the TPAT backsheet and an 

offset between the circuit plate and the frame (see Figure 5). The combination of improperly 

used tape during laminate lay-up and dirt buildup on obsolete wide frames could explain 

performance variation from virtually no loss to significant losses. 

18 
Tape 

Figure 17. Improperly used tape inside the package. 

One of the modules from the array at NREL that showed a degraded FF was dissected expecting 

that lay-up tape would be found and explain the loss in FF. The frames were removed and the 

edge of the laminate was inspected. Although indentations in the backsheet due to proper use of 

lay-up tape were found, inspection of the edge gave no indication of improperly used lay-up 

tape. The EVA was cut and removed from the step formed by the edge of the circuit plate and 

the front plate thereby exposing the edge of the laminated circuit plate. No areas of poor 

adhesion between the EVA and the back edge of the circuit plate were observed by attempting to 

lift the EVA with a utility knife. This testing indicted no improper use of lay-up tape for this 

particular module. 

Adhesion between the backsheet and the circuit plate was also tested by cutting into the EVA 

parallel to the circuit plate to release a section of the backsheet and then peeling back the 

backsheet. Lower adhesion of the TPAT along one of the long edges of the circuit plate was 

observed along with the odor of EVA. These subjective observations may indicate incomplete 

curing of the EVA leading to lower interface adhesion and thereby higher moisture ingress. 

Also, glass to EVA adhesion is know to be dependent on EVA curing and the bond between 

EVA and glass is mechanical rather than chemical although “primers” are added to the EVA to 

improve adhesion. In addition to EVA curing, EVA quality, priming, glass surface quality or 

other lamination and packaging issues could have lead to the lower adhesion of the TPAT along 

one edge and the odor of EVA. In addition, the ability of the frames to help maintain a physical 

bond through compression, directly inhibit water vapor penetration or avoid trapping water may 

depend on these packaging details and the indentations in the backsheet from “proper” use of 

lay-up tape. Therefore, packaging issues, the use of lay up tape and other details of the 

lamination and framing processes, may have contributed to failure for some but not all modules. 

19 
Laser scanning results published by NREL indicate degradation due to shunting primarily at the 

edge of modules, which is consistent with an interpretation that packaging issues lead to 

degradation [19]. Reverse bias hot spot measurements made at NREL using a technique based 

on observing discoloration of heat sensitive sheets indicated hot spots throughout some degraded 

modules. However, a correlation between the qualitative hot spot data and the modules that 

degraded could not be established since similar data before degradation was not available, the 

link between forward bias FF and reverse bias hot spots is tenuous, and a comparison could not 

be made between hot spots and modules with and without degradation. These hot spot 

measurements do not seem to clearly contradict the laser scan results indicating a packaging 

issue. 

Figure 18. A laser scan of a thin-film module showing shunting at the edges (Figure 8. from 

reference 19 ). 

Information generated in conjunction with the development of a new glass/glass package, with 

no TPAT backsheet, was considered to explain degradation for some modules made using the 

package design incorporating a TPAT backsheet. As discussed in the preceding section, 

broadening and darkening of interconnects, Figure 12, has been found to be an indicator of 

power losses characterized by lower current due to gross moisture ingress. No darkening and 

broadening of the interconnects was observed for the dissected module from the array at NREL 

that lost FF. Smaller (ST10) modules retrieved for nondestructive and destructive testing may 

have had barely detectable corrosion along the edge of cells but not the darkening and 

broadening observed for the prototype glass/glass package. Also, the electrical performance 

change with darkening and broadening of the interconnects is a drop in current rather than an 

decrease in FF. Therefore, high water vapor ingress and a decrease in Isc does not seem to be 

the cause of degradation for the subset of modules deployed with a TPAT backsheet. This does 

20 
not contradict the possibility that a lower degree of water vapor ingress could be responsible for 

the decreases in FF. 

Array data from test sites throughout the country is consistent with and augments the information 

obtained from individual modules and the NREL array. Figure 19 is a chart of average annual 

decline in power for 32 module arrays deployed at: 

“FSEC” ` - Florida Solar Energy Center, Cocoa, FL 

“Wisconsin” - University of Wisconsin, Madison, Wisconsin 

“Gumbo” - Gumbo Limbo Environmental Education Center & Florida Atlantic 

University, Boca Raton, Florida 

“NREL” - National Renewable Energy Laboratory, Golden, Colorado 

“Austin” -University of Texas at Austin, Austin, Texas 

“SWTDI” - Southwest Technology Development Institute, Las Cruces, New Mexico 

These test site locations represent diverse climates and, as indicated in the figure, two main 

module configurations, wide and narrow frames, are included in the data. The two module 

configurations are equally well described as two production timeframes. The average annual 

decline ranges from slightly negative, an improvement, through minimal changes to significant 

losses. If there is a climatic component of the changes, it is obscured by other variation. 

However, a hot humid environment, which would be expected to be the harshest, is not necessary 

for changes and, in fact, the array showing a small improvement is from an area (Austin) selected 

for array deployment because of the hot and humid environment. Avg. Annual Decline (%) 

10 

8 

6 

4 

2 

0 

-2 

FSEC Wisconsin Gumbo NREL Austin SWTDI 

Wide Frame Narrow 

Frame 

Array Location 

Figure 19. 32 Module Arrays: Average Annual Decline 

21 
The presence of any significant loss is best correlated with module configuration or timeframe 

[17]. This correlation is also consistent with long-term outdoor stability testing for individual 

modules, Figure 13, where multiple prototype package designs have demonstrated long-term 

stability. The possible exceptions are the two modules deployed in 1998, which is the same 

timeframe as the arrays that exhibit losses. Losses are not inherent since multiple past and 

present arrays have demonstrated stability, a range of array performance from improvement 

through losses is observed for the timeframe where arrays might show significant losses and 

within the arrays that show losses there is a range of module performance including no loss. 

Some failure mechanisms, such as improper use of lay-up tape and dirt buildup for wide frames, 

have been clearly demonstrated. Other subjective observations imply that additional circuit plate 

or packaging process variables may have effected long-term stability for pre-production modules 

produced in the timeframe when wide frames were standard. 

22 
Conclusions 

Outstanding progress has been made in the initial commercialization of high performance thin 

film CIS technology. The following are highlights of accomplishments during this subcontract 

period: 

• Executing SSI’s process continues to demonstrated predictability of the CIS process. 

• Cumulative production for 2002 exceeded 1 MW - about twice the production rate for 2001 

• Average laminate efficiency for 2002 is 10.8% with a full width of only 12% of the average. 

• Dramatic increases in line yield from improved production protocols and addressing 

disparate special causes for process variation. 

• Line yield increased from about 60% in 2000 to about 85% in 2002. 

• NREL confirmed a champion 12.8 percent aperture area conversion efficiency for a large 

area (3626 cm2

) CIS production module. 

• Significant progress was made toward developing a “glass/glass” package that eliminates the 

TPAT backsheet for decreased cost, simplification of the package and decreased operating 

temperature 

• Field failure mechanisms for prototype modules have been clearly demonstrated. Additional 

circuit plate or packaging process variables also effected long-term stability for preproduction modules. 

• Very promising preliminary results for edge seal developed in collaboration with the new 

NREL sponsored National Thin-Film PV Module Reliability Team. 

• Long-term outdoor stability has been demonstrated at NREL where ~30x30 cm and ~30x120 

cm modules with multiple prototype package designs have undergone testing for over 

fourteen years. 

The demonstrated high line yield as the result of process R&D is the major accomplishment. No 

one major process improvement was responsible for the yield improvements. Dramatic 

improvements in yield were the result of improving production protocols and addressing 

disparate special causes for process variation. This major accomplishment supports attractive 

cost projections for CIS. SSI's thin-film CIS technology is poised to make very significant 

contributions to DOE/NREL/NCPV long-term goals - higher volume, lower cost commercial 

products. 

Further device and production R&D can lead to higher efficiencies, lower cost, and longer 

product lifetime. Prerequisites for commitment to large-scale commercialization have been 

demonstrated at successive levels of CIS production. Remaining R&D challenges are to scale 

the processes to even larger areas, to reach higher production capacity, to demonstrate in-service 

durability over longer times, and to advance the fundamental understanding of CIS-based 

materials and devices with the goal of improvements for future products. SSI's thin-film CIS 

technology is poised to make very significant contributions to DOE/NREL/NCPV long-term 

goals - higher volume, lower cost commercial products. 

23 
References 

1. D. Tarrant, R. Gay, “Research on High-Efficiency, Large-Area CuInSe2-Based Thin-Film 

Modules, Final Subcontract Report, 16 August 1993 – 30 June 1995”, NREL/TP-413-8121, 

1995. 

2. D. Tarrant, R. Gay, "Thin-Film Photovoltaic Partnership Program - CIS-based thin film PV 

Technology. Final Technical Report, September 1995 through December 1998", (October 

1999) NREL report NREL/SR-520-27148. 

3. D. Tarrant, R. Gay, "Thin-Film Photovoltaic Partnership Program - Commercialization of 

CIS-Based Thin-Film PV. Final Technical Report, August 1998 - November 2001", August 

2002, (NREL/SR-520-32772). 

4. M. Contreras, et. al. “Progress Toward 20% Efficiency in Cu(In,Ga)Se2 Polycrystalline ThinFilm Solar Cells”. Progress in Photovoltaics: Research and Applications. Vol. 7, 1999; pp. 

311-316; NICH Report No. JA-520-26111. 

5. R. Gay, “Prerequisites to Manufacturing Thin-film Photovoltaics”, Thin Film Photovoltaic 

Symposium, IEC, May 1997. Published in Progress in Photovoltaics: Research and 

Applications, 5 (1997) pp. 337-343. 

6. Dale E. Tarrant and Robert R. Gay, “Early Experience with Manufacturing CIS Products”, 

National Center for Photovoltaics, Program Review Meeting, April 16-19, 2000, Denver, 

Colorado. 

7. Robert R. Gay and Franz H. Karg, “Experience with Manufacturing CIS Products”, 

Euroconference “Photovoltaic Devices: Thin Film Technology”, Berlin (Teltow), Germany. 

8. C. L. Jensen, D. E. Tarrant, J. H. Ermer, G. A. Pollock, "The Role of Gallium in CuInSe2 

Solar Cells Fabricated by a Two-Stage Method", Proc. 23rd IEEE Photovoltaic Specialists 

Conference, Louisville, Kentucky, May 10-14, 1993, pp. 577-580. 

9. D. Tarrant, J. Ermer, "I-III-VI2 Multinary Solar Cells Based on CuInSe2", Proc. 23rd IEEE 

Photovoltaic Specialists Conference, Louisville, Kentucky, May 10-14, 1993, pp. 372-378. 

10. R. Gay, M. Dietrich, C. Fredric, C. Jensen, K. Knapp, D. Tarrant, D. Willett, "Efficiency and 

process Improvements in CuInSe2-Based Modules", Proc. 12th European Photovoltaic Solar 

Energy Conference, Amsterdam, The Netherlands, April 1994, pp. 935-938. 

11. R. Wieting, D. DeLaney, M. Dietrich, C. Fredric, C. Jensen, D. Willett, “Progress in CISBased Photovoltaics through Statistical Process Control”, Proc. 13th European Photovoltaic 

Energy Conference, Nice, France, October, 1995, 1627-1630. 

12. R. Wieting, "The Application of Statistical Process Control to the Development of CIS-Based 

Photovoltaics", 13th NREL Photovoltaics Program Review, Lakewood, Colorado, May 1995. 

Published in AIP Conference Proceedings 353, (1996), pp. 19-25. 

13. Wheeler, Donald J.; Chambers, David S. (1992). Understanding Statistical Process Control, 

2nd edition. Knoxville, TN: SPC Press. 

14. D. Tarrant, R. Gay, “High Yield CIS Production - Progress & Perspectives”, National Center 

for Photovoltaics and Solar Program Review Meeting – 2003, March 24-26, 2003. 

24 
15. D. E. Tarrant, R. R. Gay, V. Probst, F. H. Karg “CIS Thin Film Development and Production 

Status at Shell Solar, May 2003”, 3rd World Conference on Photovoltaic Energy Conversion, 

May 11 - 18, 2003, Osaka, Japan 

16. Supported by NREL Subcontract # NDO-1-30628-06, “PV Manufacturing R&D, Integrated 

CIS Thin-Film Manufacturing Infrastructure”. 

17. Voss, Steve, “Accelerated Environmental Testing of Shell Solar CIS”, National Thin-Film 

Module Reliability Team Meeting, Florida Solar Energy Center, Cocoa, FL., February 27-28, 

2003. 

18. J. R. Sites, “Device Physics of Thin-Film Polycrys-talline Cells and Modules, Phase I Annual 

Report”, NREL/SR-520-27663, December, 1999, p 16. 

19. Emery, Keith, “Nondestructive Performance Characterization Techniques for Module 

Reliability”, NCPV and Solar Program Review Meeting 2003 NREL/CD-520-33586 Page 

954. 

25 
REPORT DOCUMENTATION PAGE Form Approved 

OMB NO. 0704-0188 

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1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE 

March 2004 

3. REPORT TYPE AND DATES COVERED 

Annual Technical Report, 24 April 2002–23 April 2003 

4. TITLE AND SUBTITLE 

Process R&D for CIS-Based Thin-Film PV: Annual Technical Report, 

4 April 2002–23 April 2003 

5. FUNDING NUMBERS 

PVP45001 

ZDJ-2-30630-16 

6. AUTHOR: 

D.E. Tarrant and R.R. Gay 

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 

Shell Solar Industries 

4650 Adohr Lane 

Camarillo, California 93011-6032 

8. PERFORMING ORGANIZATION 

REPORT NUMBER 

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 

National Renewable Energy Laboratory 

1617 Cole Blvd. 

Golden, CO 80401-3393 

10. SPONSORING/MONITORING 

AGENCY REPORT NUMBER 

NREL/SR-520-35684 

11. SUPPLEMENTARY NOTES 

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12b. DISTRIBUTION CODE 

13. ABSTRACT (Maximum 200 words): During this subcontract period, predictability of Shell Solar Industries’s CIS process was demonstrated 

by continuously executing the process while increasing throughput. Cumulative production for 2002 exceeded 1 MW - about twice the 

production rate for 2001. Average laminate efficiency for 2002 is 10.8% with a full width of only 12% of the average. Dramatic increases 

in line yield were achieved from improved production protocols and by addressing disparate special causes for process variation. Line 

yield increased from about 60% in 2000 to about 85% in 2002. NREL confirmed a champion 12.8 % aperture-area conversion efficiency 

for a large-area (3626 cm2

) CIS production module. Field failure mechanisms for prototype modules were clearly demonstrated. 

Additional circuit-plate or packaging process variables, although not as clearly established, were also found to affect long-term stability 

for pre-production modules. Significant progress was made toward developing a “glass/glass” package that eliminates the TPAT backsheet 

for decreased cost, simplification of the package, and decreased operating temperature. Very promising preliminary results were 

demonstrated for edge seals developed in collaboration with the new NREL-sponsored National Thin-Film PV Module Reliability Team. 

Long-term outdoor stability has been demonstrated at NREL where ~30x30 cm and ~30x120 cm modules with multiple prototype package 

designs have undergone testing for over 14 years. The demonstrated high line yield is the major accomplishment. No one major process 

improvement was responsible for the yield improvements. Judicious application of manufacturing engineering disciplines such as SPC, 

analysis of variation, and design of experiments led to a clear definition of near-term yield issues. Dramatic improvements in yield were 

the result of improving production protocols and addressing disparate special causes for process variation. This major accomplishment 

supports attractive cost projections for CIS. Process R&D at successive levels of CIS production has led to the continued demonstration of 

the prerequisites for commitment to large-scale commercialization. 

14. SUBJECT TERMS: PV; module; device; manufacturers; copper indium diselenide (CIS); 

thin film; encapsulated module; deposition process; monolithic; large-area reactor; 

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OF REPORT 

Unclassified 

18. SECURITY CLASSIFICATION 

OF THIS PAGE 

Unclassified 

19. SECURITY CLASSIFICATION 

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Unclassified 

20. LIMITATION OF ABSTRACT 

UL 

NSN 7540-01-280-5500 Standard Form 298 (Rev. 2-89) 

Prescribed by ANSI Std. Z39-18 

298-102